This invention relates to the production of polyvinyl chloride plastisol and organosol coating compositions which exhibit improved adhesion when fused on glass, metal and fabric substrates. In particular, it relates to such coating compositions containing a hydrolysis product of an aminofunctional organotrialkoxysilane.
Polyvinyl chloride (PVC) plastisols are dispersions in plasticizers of fine particle size PVC resins. The plasticizers are simply organic solvents that solubilize the resin at elevated temperatures to give a homogeneous melt that cools to a tough flexible vinyl product. Volatile liquids are sometimes included in the compositions to reduce viscosity in which case the dispersions are referred to as organosols. It is well known that coatings may be formed on many substrates by applying a PVC plastisol or organosol to the surface of the substrate and heating the combination until the plastisol or organosol fuses. Upon cooling a tough homogeneous coating is obtained.
One problem that has limited the application of PVC plastisol and organosol coating compositions is the poor adhesion of the coatings to many surfaces. Many attempts have been made to improve the adhesion of the coatings. Treatment of the surfaces with primers before applying the coating is known to improve adhesion, but is often commercially undesirable because of an additional process step involved. Alternatively, several adhesion promoting additives have been suggested for use in plastisol coating compositions. Such additives as phenolic resin and vinyl chloride-vinyl acetate copolymers have been used in plastisol compositions but in many cases the adhesion of the coatings is not as high as would be desirable. On many instances the additives may result in undesirable side effects such as excessive increases in viscosity of the compositions during storage.
It is also known from U.S. Pat. No. 3,998,985 and Great Britain Pat. No. 952,991 to add a mixture of an amino-organosilicon compound and an organic epoxide compound to PVC plastisols to improve the adhesion of coatings to glass and metal surfaces. Also in Great Britain Pat. No. 1,113,635 it is taught that adding an amino-organoalkoxysilane without an epoxy compound to a PVC plastisol or organosol improves the adhesion of a coating.
More specifically, it is stated in U.S. Pat. No. 3,248,358 that adherent coatings can be produced from compositions containing vinyl halide polymer, an organic solvent and an amino-organosilicon compound (i.e., a hydrocarbonoxysilane or a siloxane). It is further taught that it is desirable to reduce the amount of amino-organosilicon compound required in the composition to obtain the desired adhesion for both economic reasons and to reduce the amount of discoloration caused by the amino-organosilicon compound. One such method is taught in U.S. Pat. No. 3,248,358, in which the vinyl halide resin and the amino-organosilicon compound are mixed prior to incorporation of the vinyl halide resin into the plasticizer to form the plastisol or organosol. This method of employing the amino-organosilicon compound requires a separate process step to treat the PVC resin before a plastisol is formed. In many cases it would be more advantageous if the PVC plastisol user could simply modify a conventional PVC plastisol to obtain the coating adhesion required for a particular application.
Accordingly, it is a purpose of the present invention to provide an improved method of employing amino-organosilicon compounds to modify a conventional PVC plastisol after the PVC resin and plasticizer have been combined to form the plastisol. Further it is a purpose of the present invention to provide a method of further improving the adhesion of PVC plastisol coatings while employing minimum amounts of the amino-organosilicon compounds. It is also a purpose of the present invention to reduce such undesirable side effects as viscosity increase in the plastisol and discoloration in the coating while maintaining the improved adhesion of the coating.
It is known from U.S. Pat. No. 3,350,345 to partially hydrolyze functional organoalkoxysilanes including aminofunctional organoalkoxysiloxanes prior to treating siliceous filler surfaces with the silanes to improve the adhesion of the filler surfaces to rubber. One of the ways disclosed for treating siliceous fillers was separate addition to the rubber of the partially hydrolyzed silane and the siliceous filler. There is no suggestion in this patent that employing the partially hydrolyzed silane in polymers other than the synthetic or natural rubbers recited therein would result in better adhesion than employing the unhydrolyzed silane. British Pat. No. 1,485,517 suggested similar prehydrolyzed silanes as improved primers to facilitate adhesion between composite materials. The materials mentioned included polyvinyls as well as many others. This patent does not suggest that prehydrolyzed silanes could be incorporated in the polymer compositions in any way to increase the adherence of coatings of the polymers to substrates.